Social networking services (e.g., Facebook® and Twitter®) and blog services are widely used worldwide. Via such social networking services and/or blog services, users freely post descriptions of their online activity, their ideas and/or opinions, images and/or videos, news, and/or any other digital content that they want to share with others. As information sharing via social networking services and/or blog services becomes popular, it becomes highly possible for the users to be exposed to unwanted information.